1. Field of the Invention
The present invention relates to a contact hole structure with respect to a word line of a semiconductor memory.
2. Description of the Related Art
In recent years, many electronic devices using a NAND flash memory as a main storage memory have been produced commercially. On the other hand, improvement in capacity of storage capacity of a NAND flash memory is demanded as the function of an electronic device is varied, so that shrink of a memory cell and complication of a manufacturing process accompanied therewith result in the subject to be solved (for instance, refer to Jpn. Pat. Appln. KOKAI Publication Nos. 2002-184875, 5-88375, and 8-55920).
For instance, shrink of a memory cell conspicuously proceeds; however, in order to achieve improvement in reliability of the memory cell while eliminating problems such as cutting or short-circuiting of conductive lines or dispersion of contaminants caused by fabrication of the memory cells, with respect to conductive lines and contact holes, determination of sizes and pitches, or setting of processing condition should be performed in consideration of misalignment at the time of photolithography.
In addition, the word lines are formed with a feature size, which is a minimum size by a photolithography technique in each generation, by a pattern of lines and spaces. But, for instance, the conductive lines made of metal should be arranged on the word lines, and the conductive lines should be connected to the word lines via a contact hole in order to connect the word lines to a word line driver.
However, although with respect to the contact hole, examination on lateral displacement such as aligning accuracy at the time of the photolithography has been made sufficiently, examination on longitudinal displacement such as etching depth has not been made sufficiently.
In addition, practically, there occur many defects considered to be affected by depth of the contact holes with respect to the word lines, and therefore ascertaining the cause of the defects and developing a technology to solve it is an indispensable object.
Meanwhile, the same object occurs not only in the NAND flash memory but also in other semiconductor memories in which improvement in capacity of storage capacity is demanded.